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G.I & Nutrition > Normal Physiology Small Bowel and Colon > Flashcards

Normal Physiology Small Bowel and Colon Flashcards

1
Q

What is the mode of primary motility in the small bowel?

A

segmentation in the fed state –> peristaltic graident via pacemaker cells 9-12 contractions/min –> transit 3-5 hours

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2
Q

What is the gastroileal reflex?

A

gastrin activates segmentation in ileum

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3
Q

What is the intrinsic reflex arc?

A

mechanoreceptors activate motility in small bowel

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4
Q

What is the migrating motor complex?

A

occurs during fasting state –> sequential organized short waves initiated by motilin in ileum –> accompanied by pyloric sphincter relaxation

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5
Q

What initiates the migrating motor complex?

A

motilin in ileum

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6
Q

What turns off the migrating motor complex?

A

gastrin secretion (meal time)

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7
Q

Where is the vomiting center?

A

medulla: lateral reticular formation

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8
Q

What are the vomiting afferents?

A

irritant receptors in gut and other organs

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9
Q

What are the vomiting efferents?

A

vagal, phrenic, spinal, S, P/S

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10
Q

Mechanism of vomiting

A

saliva –> upper intestine contraction –> pylorus contraction –> abdominal muscles/diaphragm contraction –> LES/esophagal dilation –> glottis closes

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11
Q

Does the small bowel secrete enzymes?

A

no –> water and mucus for hydrolysis and lubrication (driven by Cl- secretion)

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12
Q

What drives small bowel secretion?

A

Cl- secretion in crypts

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13
Q

What regulates small bowel secretion?

A

cAMP

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14
Q

What is the primary channel involved in small bowel secretion?

A

CFTR

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15
Q

How is small bowel absorption regulated?

A

it is not –> absorbs everything isotonically and doesn’t concentrate the stuff unlike the kidney

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16
Q

2 types of surface epithelial cells in small bowel

A

villus and crypt cells of lieberkuhn

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17
Q

What is the function of villi?

A

absorption

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18
Q

What is the function of crypts?

A

secretion of Cl-

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19
Q

What is the average lifespan of intestinal epithelia?

A

3 days

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20
Q

What enzyme initiates digestion of carbohydrates?

A

salivary amylase

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21
Q

What carbohydrate digestion occurs in small bowel?

A

pancreatic amylase secretion and degradation of complex carbs to disaccharides –> final step = brush border disaccharidases

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22
Q

How are sugars transported in the small bowel?

A

cotransport with Na+

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23
Q

What enzyme initiates digestion of proteins?

A

HCl-pepsin in stomach

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24
Q

What protein digestion occurs in small bowel?

A

pancreatic proenzymes activated in lumen –> enterokinase catalyzes trypsinogen –> protease activation –> final step = brush border aminopeptidases

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25
Q

How are proteins transported in the small bowel?

A
  1. cotransport with Na+ w/ carriers for neutral basic and acid AAs
  2. cotransport of di/tripeptides with H+ and broken down into AAs in enterocyte
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26
Q

What happens to fat in the lumen of the small bowel?

A

emulsification/digestion

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27
Q

How is lipid absorbed by the small bowel?

A

micell transfer across apical cell membrane

28
Q

What happens to lipids in enterocytes?

A

processing and reconstitution into bigger lipid molecules for lymphatic/bloodstream export

29
Q

What lipodigestive mechanisms take place in the stomach?

A
  1. gastric lipase breaks down TG –> FA and DG

2. DG and phospholipids stabilize emulsion

30
Q

What lipodigestive mechanisms take place in the duodenum?

A
  1. bile salts stabilize emulsion

2. pancreatic lipase converts TG –> FA + MG

31
Q

What is inside a stable duodenal emulsion?

A

tg, dg, cholesterol, fat soluble vitamines

32
Q

What is outside a stable duodenal emulsion?

A

Phospholipids, MG, FA, bile salts –> hydrophilic

33
Q

What is colipase and where is it secreted?

A

pancreas –> brings lipase and TG together –> 50% decrease in lipase function without colipase

34
Q

What is phospholipase A2 and where is it secreted?

A

pancreas –> digests phospholipids on emulsion surface, helps anchor lipase to emulsion, activated by bile salts

35
Q

What activates phospholipase A2

A

bile salts

36
Q

Do brushborder enterocytes digest fat?

A

no

37
Q

What is the fate of bile salts?

A

some excreted but much of it eventually reabsorbed in terminal ileum

38
Q

How are fats packaged for transport to lymphatics?

A

chylomicrons coated with ApoA,B –>exocytic release

39
Q

How are vitamins digested?

A

they are not –> absorbed whole

40
Q

What are the fat soluble vitamins?

A

ADEK

41
Q

How is B12 absorbed?

A

IF from gastric parietal cells transport B12 from proximal bowel to ileum where IF-B12 complex is absorbed via transport protein at terminal ileum

42
Q

How are water soluble vitamins absorbed?

A

B, C via simple diffusion or carrier mediated transport

43
Q

Where does B12 bind intrinsic factor?

A

in proximal small bowel after bieng freed from carrier R protein

44
Q

Relative rate of absorption of salt/water in three parts of small bowel?

A

ileum > jejunum > duodenum

45
Q

How is salt/water absorbed in small bowel?

A

actively absorbed via Na+/K+ Atpase on basolateral membrane

46
Q

Is there more Na in the: lumen, cell, blood

A

blood

47
Q

Is there more K in the: lumen, cell, blood

A

cell

48
Q

What is the voltage of the lumen

A

-4mv

49
Q

What is the voltage of an enterocyte?

A

-60mv

50
Q

What is the voltage of blood next to an enterocyte?

A

0mv

51
Q

Functions of colon

A

salt and water absorption (no contentration), waste storage, no digestion

52
Q

<p>

| What is more permeable to ions? small/large bowel</p>

A

<p>

| small bowel</p>

53
Q

What ions are absorbed in colon?

A

Na/Cl/water

54
Q

What ions are secreted in colon?

A

K+ (unlike small bowel), HCO3

55
Q

What is more permeable to water? small/large bowel

A

colon is slower and absorbs less

56
Q

Small bowel or colon? digestion

A

SB

57
Q

Small bowel or colon? na/nutrient transport

A

SB

58
Q

Small bowel or colon? K secretion

A

colon

59
Q

Small bowel or colon? net hco3 secretion

A

large bowel

60
Q

Small bowel or colon? water absorption

A

sb > colon

61
Q

Small bowel or colon? concentration

A

neither

62
Q

What regulates segmentation?

A

ANS

63
Q

What is the gastrocolic reflex?

A

simultaneous strong contractions in proximal colon –> mass movement response to gastrin and extrinsic nerves

64
Q

What is secreted by bacteria that nourishes colon?

A

SCFA (short chain fatty acid), gas, vitamin K, stimulate immunity/IgA secretion

65
Q

T/F defecation involves both voluntary and involuntary muscles

A

T

G.I & Nutrition (43 decks)

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